Numerous container designs in the past have incorporated structures for allowing the stacking of a plurality of containers in a column so as to increase packing efficiency or to eliminate relative transverse sliding therebetween. One example of stackable containers are common household plastic tubs having lids with recesses thereon, the base of the tub above fitting into the recess. The design of most stackable containers is simply to allow one container to be placed on top of another and an assumption is made that the stack will remain vertical and stable.
Some stackable containers are design to mate together to more securely maintain the vertical stack. One such design is shown in a small polyethylene stackable container with the trade name STACK PAK, manufactured by ULTRATEK of Salt Lake City, Utah. The STACK PACK container has a base with a lid attached to one side by a connecting flap. The top of the lid includes a circular step around the circumference of which is a small outwardly protruding ridge. The bottom of the base of the container includes a rim portion which has an inner diameter sized to fit over the ridge on the lid step. Three small inwardly projecting detents on the inner surface of the rim of the base are sized to provide an interference fit with the ridge of the lid step.
One STAK PAK container is thus placed on top of another with the rim of the base of the top container being pressed over the lid step of the lower container so that the detents are forced below the outwardly extending ridge, providing a an interference coupling between the two containers. Although the containers are nominally held together, the interference of the detents and ridge is insufficient to withstand even moderate separating forces. A column of STAK PAK containers holding articles within is especially susceptible to breaking apart when the column is tilted, as at most only one of the detents is holding the column together, due to the wide arcs between detents. Furthermore, the detents may wear away after repeated couplings and lose effectiveness.
The STACK PAK container, as well as a number of other non-stacking small plastic containers having lids, were initially designed for taking biological specimens from humans or animals. However, the size of these containers have made them popular with young children for holding disks used in playground games. Especially popular at this time, is a playground game generically termed a milk cap game which utilizes a plurality of thin paper disks with printing on one side and at least one thicker disk for slamming down on the paper disks. The heavier slamming disks may be made of paper, hard plastic, metal, or other suitable material. The actual game is essentially a vehicle for the distribution and trading of the game disks, which are marketed with a vast array of printed styles and designs. Thus, a player may possess numerous types of game disks, as well as a selection of the thicker slammer disks. The small containers mentioned above are thus ideal for segregating the various disks and the capacity for stacking a number of containers in a column is desirable. However, the STAK PAK container is ineffective for stacking more than a few full containers together, especially when used to store the heavier disks, as the stack becomes unstable due to the aforementioned structural reasons.
There is thus a need for a stackable container which avoids the deficiencies of the prior art.